One could argue that Poe's use of syntax and diction in his short story most effectively develop the central theme of madness throughout "The Tell-Tale Heart." Syntax refers to the way words and sentences are placed together, while diction refers to an author's choice of words. In the short story, Poe's syntax is choppy, staccato, and irregular. Since the narrator is mentally deranged and neurotic, the short, broken sentences express his anxiety, and the sudden stops in the middle of the sentences reflect his distressed, excited mindset. Syntax also directly relates to the narrator's voice, and Poe is suggesting that the narrator is mentally unstable.

Poe's use of diction also helps develop the theme of madness. The narrator uses the words "disease," "hell," "blood," "evil," and "mad," which are unsettling, dark words. Repetition is also used to underscore the theme of madness as the narrator continually defends himself by claiming that he is not mad. The words "mad," "madmen," and "madness" continually show up, and it is glaringly obvious to the reader that the narrator is mentally unstable. Overall, Poe uses syntax to emphasize the narrator's anxious voice, and he uses diction to develop the theme of madness throughout his classic short story "The Tell-Tale Heart."